Cases arise where the user may want to use a higher
power stepper driver, or a step & direction controlled servo on one
or more of the axes being controlled by the ss4544 system. A hardware
option STEP&DIR is available which creates the availability of step and direction
output signals on any of the four axes.
In addition there is a ZSERVOSD option chip which provides step and direction outputs on the X and Y axis. Information on the STEP&DIR option is also found in the online help in ssDEMO and in the <Specifications>/<Mechanical>/<Limits and Options> and <Specifications>/<Electrical>/<Limits and Options> from the main menu of ssDEMO.

Note: The step and direction option chips have been redesigned to provide much better control for various servo drives and also reduce the frequency response requirements of whatever drive that is connected. STEP&DIR is now Revision D, while ZSERVOSD is at revision B. To utilize these option chips, firmware versions 661P or later are required.

1. Installing the STEP&DIR Option PAL

If you already have a STEP&DIR Rev-D option pal installed in your system you can skip this. To insert the option pal in a system, remove the ss4544 and place face down on a table with the fan toward you. Remove the 4 cap screws in the corner of the fan panel, pull off the panel and lay on table (there will still be a power cable connected to the fan). Slide out the bottom cover plate pulling toward you. You will need a little force to do this. If it is stuck, you can remove the two cap screws at the other end of the panel. Do NOT remove all four screws at the power end of the box.

You will see the location for the option pal in a socket in the middle of the controller board. Simply snap in the option pal, being careful to align the notched corner of the PAL with the notched corner of the socket. If you have to remove it for some reason, it is best done with a removal tool. If you do not have one, you can carefully pry up at the two corners with the slots for doing this. A bent paper clip can serve as a tool for this by bending out a straight section then with a pair of pliers bending a short (0.050") right angle at the tip of the straight section.

2. Enabling the Step & Direction Feature

First of all you need to be using ssXPdemo version
2.16 or later. If you do not have it you can download the latest
revision and do a reinstall to update your old version. Download
Latest Version

When you set up your motion parameters in ssDEMO,from the main menu go to <Motion
Setup>/<Axis Locking> then select the appropriate axis output driver.
Each axis may be set to output through the normal Driver or Step&Dir
outputs which will appear on the corresponding axis i/o options connector.

3. Recommended Electrical Connections

The Step pulse will appear on pin 6 labeled EPB on
the axis I/O options connector. The Direction signal will be found
on pin 5 labeled EPA. These signals are 0 to +5v TTL levels.
They can drive 8ma in the Low state. It is recommended that each
signal be twisted with +5v coming from pin 1 and connected to an opto-isolator
at the motor driver. The opto-isolator should use the +5v supplied
from the twisted pair. This will give optimum noise immunity in the
system environment. In addition for added noise immunity, the pair
may be shielded with the shield connected to the GND connection on Pin
4.
Step pulses are approximately a square wave so the width will be 1/2 the step pulse rate and may be output
up to a maximum frequency of about 2.5MHz. You can now also control the polarity of the step pulse so that the proper control edge for your driver is used.

4. Step Signal Relationship to ss4544

The STEP output is at 256 microsteps per the step
distance set in the axis motion parameters. The maximum output step
frequency is about 2.5MHz, so the maximum full step rate is about 9700
steps/second. The ss4544 using its internal drivers can output at
a full step rate of 25000 steps/second. Parameter setup using
either method of driving is the same, since the ss4544 internally uses
256 microsteps per full step all the time.
If for some reason you need a larger microstep size
because of your driver's limitations, you may simply declare a fake full
step size in your motion parameter setup. For example if you were
using a 200 step per revolution motor with a 5 pitch lead screw (5 turns
per inch), then it would take 1000 full steps to move one inch. Therefore
you would set the full step size parameter to 1x10-3 inches. If your
driver was set at 64 microsteps/step it would actually move the motor 4
times as far. Therefore you would set the stepdistance to 4x10-3.

Another way of looking at this is calculate the distance moved in your system for one step pulse to the driver. Multiply this by 256 and enter it as the STEP DIST parameter for the axis. Note that this should always be set correctly before entering any other parameters for the axis, since this number establishes the real world relationship between your machine and the internal numbers used for control.

For example, if your servo driver caused your X stage to move 2.5 microns for each step input you would multiply this by 256 to get the number to enter in the <X-Step Dist x 10-3> parameter.

1 driver step = 2.5 uM X 256 = 640 uM = 640 x 10-3 mm

So if your display units are set to millimeters (mm) you would enter the number 640 as the <X-Step Dist x 10-3> parameter for the X-axis.